This nonprovisional application claims priority under 35U.S.C. xc2xa7119(a) on Patent Application No. 2001-0058285 filed in Korea on Sep. 20, 2001, which is herein incorporated by reference.
1. Field of the Invention
The invention relates to a method for fabricating a semiconductor device having improved isolation characteristics, and more particularly, to a method for forming an isolation region in a semiconductor device, in which nitrogen ions are injected into a region of an isolation oxide film to form an oxynitride film that prevents formation of a recess at a top edge of the isolation oxide film.
2. Background of the Related Art
A related art method for forming an isolation region in a semiconductor device will be explained, with reference to the attached drawings. FIGS. 1A-1H illustrate sections showing the steps of a related art method for forming an isolation region in a semiconductor device.
Referring to FIGS. 1A, 1B, and 1C, a pad oxide film 12, and a pad nitride film 13 are successively deposited on a silicon substrate 11.
Referring to FIG. 1D, the pad nitride film 13, the pad oxide film 12, and the silicon substrate 11 are removed selectively, to form a trench. A process for isolating a region from another region (active region) on the substrate by selectively removing the substrate and the insulating film layer on the substrate to form a trench, and filling the trench with an oxide film, is referred to as STI (Shallow Trench Isolation).
Referring to FIG. 1E, an isolation oxide film 14 is deposited sufficient to fully fill the trench, and then subjected to CMP (Chemical Mechanical Polishing) to planarize at a height of a surface of the pad nitride film 13a. 
Referring to FIG. 1F, the pad nitride film 13a, and the pad oxide film 12a on the substrate 11a are removed. As shown in FIG. 1G, an entire surface of the substrate 11a is cleaned with HF solution for removing the pad oxide film, a sacrificial oxide (not shown), and impurities on the substrate 11a. In general, the sacrificial oxide is mostly used in formation of the isolation region by STI, rather than LOCOS (Local Oxidation Of Silicon).
In the foregoing cleaning for removing the sacrificial oxide film, and the like, even the isolation oxide film 14a filling the trench is also etched, forming field recesses at upper edges of the isolation oxide film 14a, which interface with the active region. This is a major cause of deteriorating characteristics of the isolation region.
Referring to FIG. 1H, a gate oxide film 15, and a polysilicon layer 16 are successively formed on an entire surface of the substrate 11a, including the trench. The polysilicon layer 16 is patterned in a following process, for use as a gate electrode.
However, the foregoing method for forming an isolation region in a semiconductor device has the following problems.
First, the progression of process steps (deposition of a gate oxide film, formation of a gate electrode, and the like) with the field recesses remaining at the upper edges of the isolation oxide film tends to cause concentration of an electric field thereto after formation of a device, to cause malfunction of the device.
Second, at the junction, there is a tendency for an excessive flow of leakage current at the field recesses arising from deeper penetration of the implant dose through the field recesses.
Third, the excessive lateral growth of Salicide (Self Aligned Silicide) in the field recess regions substantially affects device characteristics.
Fourth, polysilicon or nitride spacers may be formed to eliminate the foregoing problems, but this results in additional deposition process steps, causing many problems in the subsequent process.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
Accordingly, the invention is directed to a method for forming an isolation region in a semiconductor device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the invention, in part, is to provide a method for forming an isolation region in a semiconductor device, which can prevent formation of field recesses at upper edges of an isolation oxide film, for improving device isolation characteristics.
The invention, in part, pertains to a method for forming an isolation region in a semiconductor device includes the steps of (a) depositing a pad oxide film, and a pad nitride film on a substrate in succession, (b) selectively removing the pad oxide film, the pad nitride film, and the substrate, to form a trench, and filling the trench with an isolation oxide film, (c) injecting nitrogen ions into an entire surface of the pad nitride film, inclusive of the isolation oxide film, to form an oxynitride film in a region of the isolation oxide film, (d) removing the pad nitride film, and the pad oxide film, and (e) successively depositing a gate oxide film, and a polysilicon layer on the substrate.
The invention, in part, pertains to the step of filling the trench with an isolation oxide film in the step (b) including depositing the isolation oxide film sufficient to fully fill the trench, and planarizing the isolation oxide film to a height of a surface of the pad nitride film. The pad nitride film remaining after the formation of the trench serves as a mask for forming the oxynitride film during the injection of nitrogen ions.
The invention, in part, pertains to injecting the nitrogen ions to concentrate at a depth from a surface of the isolation oxide film in a range of about 300 xc3x85 to 500 xc3x85 during the formation of the oxynitride film. The nitrogen ions can be injected at an angle tilted in a range of about 0-45xc2x0, allowing the nitrogen ions to penetrate deeper at an interface of the active region and the isolation oxide film during the formation of the oxynitride film. The nitrogen ions can be injected at an energy of about 20 to 50 KeV and a dose of about 5xc3x971013/cm2 to 8xc3x971015/cm2. The nitrogen ion injection can be made at a step height of about 500 xc3x85-1000 xc3x85.
The invention, in part, pertains to stabilizing the oxynitride film by thermal annealing, which can be performed at a temperature range of about 800xc2x0 C. to 1370xc2x0 C. in a rapid thermal anneal carried out in a ramp type furnace for rapid temperature elevation. The annealing is performed for about 5 seconds to about 10 minutes.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.